The present invention relates to a battery pack formed by arranging and connecting a plurality of unit batteries and, more particularly, to a battery pack having a structure capable of maintaining safety and efficiency even after a long-term use.
There is known a battery pack formed by arranging a plurality of unit batteries and electrically and mutually connecting the electrodes of the unit batteries, as disclosed in Japanese Patent Application Laid-Open Publications No. 2006-339032 and No. 2007-200758, the entire contents of which are incorporated herein by reference. In this battery pack, it is preferable that the unit batteries be arranged close to each other in order to reduce the size of the entire battery pack.
In the case of, e.g., a lithium-ion battery, it is necessary to prevent entering of water in terms of characteristics of a material thereof and thus a metal unit battery case that does not transmit water is employed.
For example, in the case where an aluminum unit battery case of a sealed type that does not transmit water is employed in the lithium-ion battery, there is a possibility that gas may accumulate in the unit battery case due to a long-term use to increase the inner pressure, resulting in inflation of the unit battery case. Thus, it is necessary to estimate the deformation of the unit battery case and design the structure thereof so as to allow for the deformation. Otherwise, the battery pack may be destroyed before the end of the life of each unit battery, disabling the subsequent use.